The present invention relates to a transparent touch panel attached on the display surface of a display device such as an LCD (liquid crystal display), a CRT (cathode ray tube), a plasma display, or the like, as well as to an electronic apparatus using the transparent touch panel. The touch panel is used to input control signals into an electronic apparatus by a user pressing a certain specific region of the display surface corresponding to the signal with a pen or a finger.
A transparent touch panel (hereinafter referred to as a xe2x80x9cTTPxe2x80x9d) of the prior art is described below with reference to FIG. 7, which shows a sectional view of a conventional TTP. In FIG. 7, a first transparent conductive layer 2, typically made mainly of indium tin oxide (hereinafter referred to as xe2x80x9cITOxe2x80x9d), is formed, typically by a sputtering process, on the upper surface of a fixed substrate 1, typically made of glass. Provided on the first ITO layer 2 is a very small dot spacer 3, typically made of an insulating epoxy resin or the like, disposed at regular intervals. The ITO layer 2 is provided at the perimeter edge with an insulating pattern 4 of a certain specific width. Above the first ITO layer 2, a movable substrate formed of a transparent film, etc. having a second transparent conductive layer 5, typically ITO, on the bottom surface, is provided opposing first ITO layer 2, with insulating pattern 4 interposed between the surfaces. The upper surface of movable substrate 6 is covered with a hard coating layer 7 for protecting movable substrate 6 from getting scratched by a pressing pen or finger. Normally, the surface of movable substrate 6 having said hard coating film 7 is used as the operating surface of a TTP. The first ITO layer 2 and the second ITO layer 5 are connected with an outside circuit (not shown) through a circuit pattern 8A formed on a flexible circuit board 8, via a connection section 9, typically made of silver paste.
Operation for inputting a control signal is conducted by pushing movable substrate 6 from above in a designated position such that first ITO layer 2 and second ITO layer 5 make contact. Regions not intended for contact between layers 2 and 5 are separated by the dot spacers 3 so that no control signal input can be made from such regions. The location of the designated position is identified by the electrical resistance ratio in the first ITO layer 2 and the second ITO layer 5. In particular, the designated position is identified by an outside circuit that detects the voltage ratio when there is contact at the designated position. The resistance is measured by applying a certain specific voltage on first ITO layer 2 and second ITO layer 5 via electrodes 10A and 10B provided at both edges of the respective layers, as shown in FIG. 8.
A conventional TTP configured above using a glass plate for the fixed substrate 1, however, has various drawbacks. For example, because glass has a large specific gravity, it is relatively heavy, and furthermore, glass is easily breakable by an excessive load or a shock.
In order to evade such drawbacks, transparent resins have been tried for fixed substrate 1. An ITO layer formed on a plastic substrate, however, also has drawbacks. One drawback is that the ITO layer poorly adheres to the plastic substrate. Another problem is that the light transmittance of a TTP with a plastic substrate is relatively less than the light transmittance of a TTP with a glass substrate. The poor adhesion of the ITO layer onto the plastic substrate may lead to a broken ITO layer after repetitive use of the TTP, or to the ITO layer peeling off from the substrate. Even if the ITO layer does not peel off, uniformity in resistance of the ITO layer may deteriorate after repetitive use of the TTP.
For improving the transmittance, it has been a common practice to form a multi-layered film of inorganic compounds over the transparent plastic substrate, such as by sputtering or vacuum deposition. This increases the manufacturing cost of a TTP, however, and additionally requires expensive production facilities for manufacture of large area TTPs. Furthermore, the adhesion of the multi-layered inorganic film onto the plastic substrate is poor.
The present invention addresses the drawbacks described above, and aims to offer a TTP that is lightweight and not easily breakable. The present invention also offers an electronic apparatus using such a TTP.
A TTP of the present invention comprises:
a fixed substrate comprising transparent plastic,
an adhesion layer disposed on the fixed substrate,
an antireflection layer disposed on the adhesion layer,
a first transparent conductive layer, such as ITO, disposed on the antireflection layer,
a second transparent conductive layer, such as ITO, provided opposed to the first transparent conductive layer and spaced therefrom, and
a flexible transparent film provided on the upper surface of the second transparent conductive layer.
Because the TTP of the present invention uses a plastic fixed substrate, it is lightweight and does not break easily. The antireflection layer provided between the fixed substrate and the first ITO layer reduces the reflection of light incident to respective boundary surfaces between the fixed substrate and the first ITO layer, thus improving light transmittance. Furthermore, the adhesion layer supports the tight adhesion of the antireflection layer and the first ITO layer onto the fixed substrate, providing uniform electrical resistance in the ITO layer. Thus the present invention provides a TTP that is superior in visibility, in durability against repetitive input operations, and that has superior positional accuracy.